The present invention is directed to a solvent free silicone coating composition which cures with minimal shrinkage and a high-gloss surface.
It is common to coat various surfaces with compositions to protect the surface against environmental effects. A common coating composition is an epoxy based composition which utilizes a two-part composition which is coated on the surface by brushing, dipping or spraying. Epoxy based coating compositions have the advantage of providing a coating with a high-gloss surface. However the epoxy based coatings generally require that the two separate parts be mixed together and used within a very short period of time. If the composition is not utilized with this period of time, it will cure before it can be applied to the surface. In addition, epoxy based compositions may emit volatile organic compounds (VOC) and require care in handling.
Silicone based compositions have also been utilized for coating of surfaces to protect the surface against environmental effects. Silicone compositions offer the advantage of long life and high resistance. However due to the nature of the curing reaction for silicone compositions, the thickness of the coating may shrink causing the surface of the coating to have a matte or satin finish. It would be advantageous to provide a silicone based composition having long life and high resistance along with minimal shrinkage of the coating and a high-gloss finish.
The present invention provides a solventless, one part room temperature vulcanizable coating for coating surfaces to provide a high gloss, minimal shrinkage coating to the surface. The coating provides for easy and convenient application by conventional methods such as dipping, flow or spraying. The coating provides a guard against environmental effects along with high physical strength and adhesion achieved with a suitable blend of reinforcing and extending fillers.
In one aspect, the present invention provides for a one-part room temperature vulcanizing organopolysiloxane rubber coating composition to provide a high gloss surface coating. The composition consists essentially of the product which is obtained by mixing the following:
a) from about 20 to about 60 weight percent of one or more polydiorganosiloxane fluids of the formula
HO[(R)2SiO]n(R)2SiOH 
xe2x80x83in which R is a monovalent alkyl or alkenyl radical having 1 to 8 carbon atoms or a phenyl radical, and n has an average value such that the viscosity is from about 10 to about 10,000 centipoise at 25xc2x0 C.,
b) from 0 to about 8 weight percent of a bifunctional chain extender of the general formula
R42xe2x80x94Sixe2x80x94X2 
xe2x80x83where X is alkoxy or ketoximino and R4 is a monovalent alkyl or alkenyl radical having 1 to 8 carbon atoms or a phenyl radical;
c) from 0 to about 50 weight percent of an inorganic extending or non-reinforcing filler;
d) from about 0.5 to about 20 weight percent of an amorphous SiO2 reinforcing filler having a surface area of between about 50 to 250 m2/g and a particle size range between about 0.01 and 0.03 microns;
e) from about 3 to about 15 weight percent of one or more crosslinking agents of general formula
(X)4-mxe2x80x94Sixe2x80x94Rxe2x80x2m 
xe2x80x83where Rxe2x80x2 is an alkyl, alkenyl or phenyl radical (preferably methyl or ethyl), X is an alkyl radical with a functional group selected from carboxyl, ketoximino, alkoxy, carbonyl or amine linked directly to the silicone atom, and m is an integer of from 0 to 2;
f) from about 0.2 to about 3 weight percent of an adhesion promoter of the formula 
xe2x80x83in which R2 and R3 are independently selected from monovalent alkyl or alkenyl radicals having 1 to 8 carbon atoms or a phenyl radical which may optionally be substituted with an alkyl radical having 1 to 8 carbon atoms, b is an integer between 0 and 3, and R1 is a saturated, unsaturated or aromatic hydrocarbon radical having 1 to 10 carbon atoms which may optionally contain a functional group; and
g) from about 0.02 to about 3 weight percent of an organotin salt as a condensation catalyst.
The present invention also provides for a method of coating surfaces to provide a high gloss coating with minimal shrinkage on the surface. The method comprises applying to the surface a thin layer of the above one-part organopolysiloxane rubber composition and allowing the layer of the one-part organopolysiloxane rubber composition to cure at room temperature to a silicone elastomer.